Process for the hydrotreatment of diesel employing a concatenation of catalysts

ABSTRACT

A process for the hydrotreatment of a diesel type hydrocarbon feed containing nitrogen-containing compounds is described, comprising a first step in which the feed is brought into contact with a catalyst in its oxide form, then a second step in which the feed is brought into contact with a dried catalyst comprising at least one organic compound containing oxygen and/or nitrogen.

The present invention relates to the field of processes for the hydrotreatment of a diesel type feed using a concatenation of catalysts. The aim of the process is to produce desulphurized and denitrogenated diesel. The hydrotreatment process of the invention is particularly suitable for the hydrotreatment of feeds comprising high levels of nitrogen.

Usually, a catalyst for the hydrotreatment of hydrocarbon cuts is intended to eliminate the sulphur-containing or nitrogen-containing compounds contained therein in order, for example, to ensure that an oil product meets the required specifications (sulphur content, aromatics content, etc.) for a given application (automobile fuel, gasoline or diesel, domestic fuel, jet fuel). The composition and the use of hydrotreatment catalysts have been particularly thoroughly described in the article by B. S Clausen, H. T. Topsøe, and F. E. Massoth, published in Catalysis Science and Technology, volume 11 (1996), Springer-Verlag. The hydrotreatment catalysts generally have hydrodesulphurizing functions and hydrogenating functions based on a sulphide of metals from groups VIB and VIII.

The tightening of automobile pollution standards in the European community (Official Journal of the European Union, L76, 22^(nd) March 2003, Directive 2003/70/CE, pages L76/10-L76/19) has required refiners to reduce the sulphur content in diesel fuels and gasolines by a very large extent (a maximum of 10 parts per million by weight (ppm) of sulphur at 1^(st) January 2009, as opposed to 50 ppm on 1^(st) January 2005). Furthermore, refiners are often forced to use feeds which are more and more refractory to hydrotreatment processes, on the one hand because crudes are getting heavier and heavier and as a result contain more and more impurities, and on the other hand due to the increase in the number of conversion units in the refineries. In fact, they generate cuts which are more difficult to hydrotreat than cuts obtained directly from atmospheric distillation because of the high levels of aromatic, nitrogen-containing and sulphur-containing compounds. These cuts thus require catalysts which have hydrodesulphurizing and hydrogenating functions which are greatly improved compared with traditional catalysts.

Adding an organic compound to hydrotreatment catalysts to improve their activity is now well known to the skilled person. A number of patents protect the use of various ranges of organic compounds such as mono-, di- or poly-alcohols, which may be etherified (WO 96/41848, WO 01/76741, U.S. Pat. No. 4,012,340, U.S. Pat. No. 3,954,673, EP 0601722). Catalysts modified with C2-C14 monoesters are described in patent applications EP 466568 and EP 1046424.

Other patents show that a specific concatenation of catalysts in the same reactor may be advantageous.

Thus, patent application US 2011/0079542 discloses that replacement of a portion of a reference HDS catalyst at the head of the bed by a catalyst with a lower activity does not modify the performances of the overall charge compared with 100% reference catalyst, because over the first portion of catalytic bed, the reaction occurs on non-refractory sulphur-containing species and does not require a high performance catalyst.

Patent EP 0651041 discloses the advantage of linking together beds of catalysts with different particle shapes in a concatenation.

The present invention concerns a process for the hydrotreatment of a feed of the diesel type by using a specific concatenation of at least two different types of catalysts, which can increase the overall activity and overall stability of the hydrotreatment process compared with a hydrotreatment process using the same quantity and the same operating conditions as just one of these two types of catalysts.

The term “hydrotreatment” means reactions in particular encompassing hydrodesulphurization (HDS), hydrodenitrogenation (HDN) and hydrogenation of aromatics (HDA).

In accordance with the process of the invention, the feed is initially brought into contact with a first type of catalyst comprising phosphorus and an active phase in its oxide form, i.e. said first catalyst is prepared using a process comprising at least one calcining step after impregnation of metallic salts. This first type of catalyst is termed the “catalyst in the oxide form” or “calcined catalyst”.

The feed is then brought into contact with a second type of catalyst which has been prepared by introducing phosphorus, active phase and an organic compound containing oxygen and/or nitrogen followed by a drying step, without subsequent calcining. It should be noted that this second type of catalyst does not undergo calcining, and so the active phase is not in its oxide form. This second type of catalyst is known as an “additive-containing catalyst”.

More particularly, the present invention concerns a process for the hydrotreatment of a hydrocarbon feed containing nitrogen-containing compounds in an amount of more than 150 ppm by weight and having a weighted average temperature in the range 250° C. to 380° C., comprising the following steps:

a) bringing said hydrocarbon feed into contact, in the presence of hydrogen, with at least one first catalyst comprising an alumina support, phosphorus, and an active phase formed by at least one metal from group VIB in the oxide form and at least one metal from group VIII in the oxide form, said first catalyst being prepared in accordance with a process comprising at least one calcining step;

b) bringing the effluent obtained in step a) into contact, in the presence of hydrogen, with at least one second catalyst comprising an alumina support, phosphorus, an active phase formed by at least one metal from group VIB and at least one metal from group VIII, and at least one organic compound containing oxygen and/or nitrogen, said second catalyst being prepared in accordance with a process comprising the following steps:

i) bringing at least one component of a metal from group VIB, at least one component of a metal from group VIII, phosphorus and at least one organic compound containing oxygen and/or nitrogen into contact with the support, so as to obtain a catalyst precursor;

ii) drying said catalyst precursor obtained from step i) at a temperature of less than 200° C., without subsequent calcining; in order to obtain a hydrotreated effluent.

It has been observed that although the additive-containing catalysts of an organic compound generally have an improved hydrotreatment capability compared with catalysts without additives, these catalysts are more easily inhibited by nitrogen-containing molecules, and in particular by basic nitrogen-containing molecules contained in the feed, than catalysts without additives. This inhibition has the consequence of reducing the activity and stability of the additive-containing catalyst over time, thus reducing their hydrotreatment capability.

The Applicant has developed a process for the hydrotreatment of a diesel type feed, comprising a concatenation of catalysts which can be used to carry out, firstly, a hydrotreatment over a catalyst in its oxide form (calcined catalyst) which has a good hydrodesulphurization and hydrodenitrogenation activity. This first type of catalyst is in particular less inhibited by refractory basic nitrogen-containing molecules and thus more active in hydrodenitrogenation than an additive-containing catalyst. This means that an intense hydrodenitrogenation can be carried out in the first step of the process of the invention and thus relieves the additive-containing catalyst of the second step which is brought into contact with the effluent leaving from this first step. The hydrotreatment is then continued by bringing the feed which has been freed from a large part of its nitrogen-containing molecules and a portion of its sulphur-containing molecules into contact with an additive-containing catalyst which is particularly active in HDS, thus allowing the intense hydrotreatment to be completed. Because the feed is brought into contact with a catalyst in the oxide form before being brought into contact with an additive-containing catalyst, the additive-containing catalyst is less inhibited by nitrogen-containing molecules and thus more active and stable over time. The specific concatenation can thus protect the additive-containing catalyst which is highly active for HDS with a catalyst in the oxide form which is highly active in HDN, which has the result of increasing the overall activity and overall stability of the catalytic concatenation compared with a catalytic system containing only additive-containing catalysts. Thus, the overall activity is increased as the hourly space velocity (volume of feed which can be treated per unit time) can be increased or, alternatively, less catalyst could be used to treat the same volume of feed. In addition, because of the increase in activity, the temperature necessary to obtain a desired sulphur content (for example 10 ppm of sulphur) can be reduced. Similarly, the overall stability is increased, as the cycle time is longer.

The hydrotreatment process of the invention is particularly suitable for the hydrotreatment of feeds comprising high organic nitrogen contents, such as feeds obtained from catalytic cracking, from a coker or from visbreaking.

The process of the present invention can be used to produce a hydrotreated hydrocarbon cut, i.e. free of any nitrogen-containing compounds, and at the same time desulphurized to contents of 10 ppm of sulphur or less. The term “ppm of sulphur” (or nitrogen) as used throughout the remainder of the text means the ppm by weight with respect to elemental sulphur (or elemental nitrogen), irrespective of the organic molecule or molecules in which the sulphur (or nitrogen) is engaged. Preferably, in the process of the invention, the hydrodesulphurization conversion is more than 98%, preferably more than 99%. The specific concatenation of catalysts in the process of the invention can thus be used to carry out an intense hydrotreatment, and in particular an intense hydrodesulphurization of diesel fuels in order to obtain diesel which complies with the specifications (ULSD, Ultra Low Sulphur Diesel).

In a variation, for the catalyst of step a) or b), the metal from group VIB is molybdenum and the metal from group VIII is selected from cobalt, nickel and a mixture of these two elements.

In a variation, for the catalyst of step a) or b), the quantity of metal from group VIB is in the range 5% to 40% by weight of oxide of the metal from group VIB with respect to the total catalyst weight, the quantity of metal from group VIII is in the range 1% to 10% by weight of oxide of the metal from group VIII with respect to the total catalyst weight, and the quantity of phosphorus is in the range 0.1% to 10% by weight of P₂O₅ with respect to the total catalyst weight.

In a variation, the catalyst of step a) or b) further contains at least one dopant selected from boron and fluorine and a mixture of boron and fluorine.

In a variation, the organic compound is one or more selected from a carboxylic acid, an alcohol, an aldehyde, an ester, an amine, an aminocarboxylic acid, an aminoalcohol, a nitrile or an amide; preferably it is one or more selected from ethylene glycol, glycerol, polyethylene glycol (with a molecular weight of 200 to 1500), acetophenone, 2,4-pentanedione, pentanole, acetic acid, maleic acid, oxalic acid, tartaric acid, formic acid, citric acid and C1-C4 dialkyl succinate; particularly preferably, it comprises at least the combination of C1-C4 dialkyl succinate and acetic acid. In accordance with another particularly preferred variation, the organic compound comprises at least citric acid.

In a variation, the catalyst of step a) or b) has also undergone a sulphurizing step.

In a variation, the quantity of basic nitrogen in the feed is 50 ppm or more.

In a variation, the feed is a feed obtained from catalytic cracking, a coker or from visbreaking.

In a variation, each of steps a) and b) is carried out at a temperature in the range 180° C. to 450° C., at a pressure in the range 0.5 to 10 MPa, at an hourly space velocity in the range 0.1 to 20 h⁻¹ and with a hydrogen/feed ratio, expressed as the volume of hydrogen measured under normal temperature and pressure conditions, per volume of liquid feed in the range 50 L/L to 2000 L/L.

In a variation, step a) is carried out in a first zone containing the first catalyst which occupies a volume V1, and step b) is carried out in a second zone containing the second catalyst which occupies a volume V2, the distribution of the volumes, V1/V2, being in the range 10% by volume/90% by volume to 50% by volume/50% by volume respectively for the first and second zone.

In a variation, step i) of step b) comprises the following steps in succession:

i′) impregnating an alumina support with at least one solution containing at least one metal from group VIB, at least one metal from group VIII and said phosphorus in order to obtain an impregnated support;

i″) drying the impregnated support obtained in step i′) at a temperature of less than 180° C. without subsequent calcining in order to obtain a dried impregnated support;

i′″) impregnating the dried impregnated support obtained in step i″) with an impregnation solution comprising at least one organic compound containing oxygen and/or nitrogen in order to obtain an impregnated catalytic precursor;

i″″) allowing the impregnated catalytic precursor obtained in step i′″) to mature, in order to obtain said catalyst precursor.

In a variation, the effluent obtained in step a) undergoes a separation step in order to separate a heavy fraction and a light fraction containing the H₂S and NH₃ formed during step a), said heavy fraction then being introduced into step b).

DETAILED DESCRIPTION The Feed and the Operating Conditions

The hydrocarbon feed treated in accordance with the hydrotreatment process of the invention has a weighted average temperature (WAT) in the range 280° C. to 350° C. The WAT is defined from the temperatures at which 5%, 50% and 70% of the volume of the feed distils in accordance with the following formula: WAT=(T 5%)+2×T 50%+4×T 70%)/7. The WAT is calculated from simulated distillation values. The treated hydrocarbon feed generally has a distillation range in the range 150° C. to 500° C., preferably in the range 180° C. to 450° C.

In the remainder of the text, we shall use the convention of calling this feed diesel, but this designation is not at all restrictive in nature. Any hydrocarbon feed containing sulphur and nitrogen-containing compounds which are hydrotreatment inhibitors, and a WAT similar to that of a diesel cut may be used in the process of the present invention. The hydrocarbon feed may have any chemical nature, i.e. it may have any distribution of chemical families, in particular paraffins, olefins, naphthenes and aromatics.

Said hydrocarbon feed comprises organic nitrogen-containing and/or sulphur-containing molecules. The nitrogen-containing organic molecules are either basic, such as amines, anilines, pyridines, acridines, quinolines and their derivatives, or neutral, such as pyrroles, indoles, carbazoles and their derivatives, for example. In particular, it is the basic nitrogen-containing molecules which inhibit the hydrotreatment catalysts, and in particular the additive-containing catalysts.

The total nitrogen content (neutral and basic) in the feed is 150 ppm or more, and is preferably in the range 200 to 6000 ppm by weight, more preferably in the range 300 to 4000 ppm by weight and still more preferably in the range 400 to 4000 ppm. The basic nitrogen content is at least one third of the overall nitrogen content.

The basic nitrogen content is generally 50 ppm or higher, more preferably in the range 65 to 2000 ppm by weight and still more preferably in the range 100 to 2000 ppm.

The sulphur content in the feed is generally in the range 0.01% to 5% by weight, preferably in the range 0.2% to 4% by weight and more preferably in the range 0.25% to 3% by weight.

The treated feed generally contains very few resins; the resins content is generally less than 1% by weight.

Said hydrocarbon feed is advantageously selected from LCO (Light Cycle Oil, or light diesels obtained from a catalytic cracking unit), atmospheric distillates, for example diesels obtained from straight-run distillation of crude or from conversion units such as fluidised bed catalytic cracking, cokers or visbreaking units, or distillates obtained from fixed bed or ebullated bed desulphurization or the hydroconversion of atmospheric residues, or a mixture of said feeds as mentioned above.

The hydrotreatment process of the invention is particularly suitable for the hydrotreatment of feeds which are more difficult to hydrotreat (having a high sulphur and nitrogen content) than cuts obtained directly from atmospheric distillation of crude. The hydrotreatment process of the invention is particularly suitable for the hydrotreatment of feeds containing high levels of nitrogen, in particular a high basic nitrogen content.

Preferably, said hydrocarbon feed is selected from a LCO feed (Light Cycle Oil) obtained from fluidized bed catalytic cracking (or FCC, Fluid Catalytic Cracking) or a cut obtained from a coking or visbreaking process. This type of cut generally has the following characteristics: a sulphur content of more than 0.5% by weight, generally 0.5% to 3% by weight, a nitrogen content of more than 150 ppm, generally in the range 200 ppm to 6000 ppm by weight, and preferably in the range 300 ppm to 4000 ppm, and of this nitrogen, at least 50 ppm of compounds termed basic compounds, generally in the range 150 to 2000 ppm, and an aromatics content of more than 25% by weight, generally 30% to 90% by weight.

The process of the invention may be carried out in one, two or more reactors. It is generally carried out in fixed bed mode.

When the process of the invention is carried out in two reactors, step a) may be carried out in the first reactor traversed by the feed, then step b) may be carried out in the second reactor placed downstream of the first reactor. Optionally, the effluent from step a) leaving the first reactor may undergo a separation step in order to separate a light fraction containing H₂S and NH₃ in particular, formed during the hydrotreatment, in step a), from a heavy fraction containing partially hydrotreated hydrocarbons. The heavy fraction obtained after the separation step is then introduced into the second reactor for carrying out step b) of the process of the invention. The separation step may be carried out by distillation, flash separation or any other method which is known to the skilled person.

When the process is carried out in a single reactor, step a) is carried out in a first zone containing the first catalyst which occupies a volume V1, and step b) is carried out in a second zone containing the second catalyst which occupies a volume V2. The percentage by volume of the first zone containing the catalyst in the oxide form of step a) with respect to the total volume of the zones is preferably at least 10% by volume. The percentage by volume of the first zone containing the catalyst in the oxide form of step a) is adjusted so as to maximize the conversion of the inhibiting nitrogen-containing compounds, termed basic compounds. The distribution of the volumes, V1/V2, is preferably in the range 10% by volume/90% by volume to 50% by volume/50% by volume in the first and second zone respectively.

The metals from group VIB or group VIII used to form the active phase of the catalysts of step a) or b) may be identical or different in each of steps a) or b).

The operating conditions used in steps a) or b) of the hydrotreatment process of the invention are generally as follows: the temperature is advantageously in the range 180° C. to 450° C., preferably in the range 250° C. to 400° C., the pressure is advantageously in the range 0.5 to 10 MPa, preferably in the range 1 to 8 MPa, the hourly space velocity (defined as the ratio of the volume flow rate of feed to the volume of catalyst per hour) is advantageously in the range 0.1 to 20 h⁻¹, preferably in the range 0.2 to 5 h⁻¹, and the hydrogen/feed ratio, expressed as the volume of hydrogen, measured under normal temperature and pressure conditions, per volume of liquid feed, is advantageously in the range 50 L/L to 2000 L/L. The operating conditions in steps a) and b) may be identical or different. Preferably, they are identical.

Step a): Hydrotreatment with a Catalyst in the Oxide Form

In step a) of the process of the invention, said hydrocarbon feed is brought into contact, in the presence of hydrogen, with at least a first catalyst comprising an alumina support, phosphorus and an active phase formed by at least one metal from group VIB in the oxide form and at least one metal from group VIII in the oxide form, said first catalyst being prepared using a process comprising at least one calcining step.

The catalyst used in step a) of the invention is composed of an alumina support, phosphorus and an active phase formed by at least one metal from group VIB in the oxide form and at least one metal from group VIII in the oxide form.

In general, the total quantity of metal from group VIB and metal from group VIII is more than 6% by weight, preferably in the range 10% to 50% by weight of oxides of metals from groups VIB and VIII with respect to the total catalyst weight.

The quantity of metal from group VIB is in the range 5% to 40% by weight, preferably in the range 8% to 35% by weight, and more preferably in the range 10% to 30% by weight of oxide of metal(s) from group VIB with respect to the total catalyst weight.

The quantity of metal from group VIII is in the range 1% to 10% by weight, preferably in the range 1.5% to 9% by weight, and more preferably in the range 2% to 8% by weight of oxide of metal from group VIII with respect to the total catalyst weight.

The metal from group VIB present in the active phase of the catalyst used in the hydrotreatment process of the invention is preferably molybdenum.

The metal from group VIII present in the active phase of the catalyst used in the hydrotreatment process of the invention is preferably selected from cobalt, nickel and a mixture of these two elements.

Preferably, the active phase of the catalyst used in step a) is selected from the group formed by the following combination of elements: nickel-molybdenum, cobalt-molybdenum and nickel-cobalt-molybdenum.

The molar ratio of the metal from group VIII to the metal from group VIB in the catalyst in the oxide form is preferably in the range 0.1 to 0.8, preferably in the range 0.15 to 0.6, and more preferably in the range 0.2 to 0.5.

Said catalyst of step a) also comprises phosphorus as a dopant. The dopant is an element which is added which in itself does not have any catalytic character, but which increases the catalytic activity of the active phase.

The quantity of phosphorus in said catalyst for step a) is preferably in the range 0.1% to 10% by weight of P₂O₅, preferably in the range 0.2% to 8% by weight of P₂O₅, more preferably in the range 0.3% to 8% by weight of P₂O₅.

The molar ratio of phosphorus to metal from group VIB in the catalyst for said step a) is 0.05 or more, preferably 0.07 or more, more preferably in the range 0.08 to 0.5.

The catalyst used in step a) of the invention may advantageously further contain at least one dopant selected from boron and fluorine and a mixture of boron and fluorine.

When the hydrotreatment catalyst used in step a) contains boron, the content is preferably in the range 0.1% to 10% by weight of boron oxide, preferably in the range 0.2% to 7% by weight of boron oxide, highly preferably in the range 0.2% to 5% by weight of boron oxide.

When the hydrotreatment catalyst used in step a) contains fluorine, the fluorine content is preferably in the range 0.1% to 10% by weight of fluorine, preferably in the range 0.2% to 7% by weight of fluorine, highly preferably in the range 0.2% to 5% by weight of fluorine.

The support is an alumina support, i.e. it contains alumina, and optionally metals and/or dopant(s), which have been introduced separately from the impregnations (for example introduced during preparation (mixing, peptizing etc.) of the support or during its shaping). The support is obtained after shaping (for example by extrusion) and calcining, in general between 300° C. and 600° C.

Preferably, the support is constituted by alumina, preferably extruded alumina. Preferably, the alumina is gamma alumina; more preferably, said alumina support is constituted by gamma alumina.

The pore volume of the amorphous support is generally in the range 0.1 cm³/g to 1.5 cm³/g, preferably in the range 0.4 cm³/g to 1.1 cm³/g. The total pore volume is measured by mercury porosimetry in accordance with ASTM standard D 4284-92 with a wetting angle of 140°, as described in the work by Rouquerol F.; Rouquerol J.; Singh K, “Adsorption by Powders & Porous Solids: Principle, methodology and applications”, Academic Press, 1999, for example instrument from the firm Microméritics™, model Autopore III™.

The specific surface area of the amorphous support is generally in the range 5 m²/g to 400 m²/g, preferably in the range 10 m²/g to 350 m²/g, more preferably in the range 40 m²/g to 350 m²/g. The specific surface area is determined in the present invention by the BET method, which method is described in the work which is cited above.

Said alumina support is advantageously in the powder form or is shaped into beads, extrudates, pellets, or irregular and non-spherical agglomerates the specific shape of which may be the result of a crushing step. Highly advantageously, said support is in the form of extrudates.

A catalyst in the oxide form used in step a) may be prepared using any method which is well known to the skilled person.

The metals from group VIB and from group VIII of said catalyst may advantageously be introduced into the catalyst at various stages of the preparation and in a variety of manners. Said metals from group VIB and from group VIII may advantageously be introduced in part during shaping of said amorphous support or, as is preferable, after said shaping.

In the case in which the metals from group VIB and from group VIII are introduced in part during shaping of said alumina support, they may be introduced in part only at the time of mixing with an alumina gel selected as the matrix, the remainder of the metals then being introduced subsequently. Preferably, when the metals from group VIB and from group VIII are introduced in part at the time of mixing, the proportion of metal from group VIB introduced during this step is 20% or less of the total quantity of metal from group VIB introduced onto the final catalyst and the proportion of metal from group VIII introduced during this step is 50% or less of the total quantity of metal from group VIII introduced onto the final catalyst.

In the case in which the metals from group VIB and from group VIII are introduced at least in part and preferably in their entirety after shaping said alumina support, the metals from group VIB and from group VIII may advantageously be introduced onto the alumina support by means of one or more excess solution impregnations onto the alumina support or, as is preferable, by one or more dry impregnations, preferably a single dry impregnation of said alumina support, with the aid of aqueous or organic solutions containing precursors of the metals. Dry impregnation consists of bringing the support into contact with a solution containing at least one precursor of said metal (metals) from group VIB and/or from group VIII, the volume of which is equal to the pore volume of the support to be impregnated. The solvent for the impregnation solution may be water or an organic compound such as an alcohol. Preferably, an aqueous solution is used as the impregnation solution.

Highly preferably, the metals from group VIB and from group VIII are introduced in their entirety after shaping said alumina support, by dry impregnation of said support with the aid of an aqueous impregnation solution containing precursor salts of the metals. The metals from group VIB and from group VIII may also advantageously be introduced by one or more impregnations of the alumina support, using a solution containing precursor salts of the metals. In the case in which the metals are introduced in a plurality of impregnations of the corresponding precursor salts, an intermediate step for drying the catalyst is generally carried out at a temperature in the range 50° C. to 180° C., preferably in the range 60° C. to 150° C. and highly preferably in the range 75° C. to 130° C.

Preferably, the metal from group VIB is introduced at the same time as the metal from group VIII, irrespective of the mode of introduction.

The molybdenum precursors which may be used are well known to the skilled person. As an example, from among the molybdenum sources, it is possible to use oxides and hydroxides, molybdic acids and their salts, in particular ammonium salts such as ammonium molybdate, ammonium heptamolybdate, phosphomolybdic acid (H₃PMo₁₂O₄₀), and their salts, and optionally silicomolybdic acid (H₄SiMo₁₂O₄₀) and its salts. The molybdenum sources may also be any heteropolycompound of the Keggin, lacunary Keggin, substituted Keggin, Dawson, Anderson or Strandberg type, for example. Preferably, molybdenum trioxide and heteropolycompounds of the Keggin, lacunary Keggin, substituted Keggin and Strandberg type are used.

The cobalt precursors which may be used are advantageously selected from oxides, hydroxides, hydroxycarbonates, carbonates and nitrates, for example. Cobalt hydroxide and cobalt carbonate are preferably used.

The nickel precursors which may be used are advantageously selected from oxides, hydroxides, hydroxycarbonates, carbonates and nitrates, for example. Nickel hydroxide and nickel hydroxycarbonate are preferably used.

In the same manner, the phosphorus may advantageously be introduced into the catalyst at various stages in the preparation and in a variety of manners. Said phosphorus may advantageously be introduced during shaping of said alumina support or, as is preferable, after shaping it. It may, for example, be introduced just before or just after peptizing the selected matrix such as, for example and preferably, the aluminium oxyhydroxide (boehmite) precursor of alumina. It may also advantageously be introduced alone or as a mixture with at least one of the metals from group VIB and VIII.

Said phosphorus is preferably introduced as a mixture with the precursors of the metals from groups VIB and group VIII, in its entirety or in part onto the shaped alumina support, preferably alumina in the extruded form, by dry impregnation of said alumina support using a solution containing precursors of the metals and the phosphorus precursor.

The preferred source of phosphorus is orthophosphoric acid, H₃PO₄, but salts and esters such as ammonium phosphates are also suitable. The phosphorus may also be introduced at the same time as the group VIB element(s) in the form of Keggin, lacunary Keggin, substituted Keggin or Strandberg type heteropolyanions.

The catalyst used in step a) of the invention may advantageously further contain at least one dopant selected from boron and fluorine and a mixture of boron and fluorine. This dopant may be introduced in the same manner as that for the phosphorus at various stages in the preparation and in a variety of manners. It may be introduced at least in part during the preparation of the support (including shaping). It may advantageously be introduced alone or as a mixture with the phosphorus or at least one of the precursors of the metals from groups VIB and VIII. It is preferably introduced as a mixture with the precursors of the metals from group VIB and from group VIII and phosphorus, in its entirety or in part onto the shaped alumina support, preferably alumina in the extruded form, by dry impregnation of said alumina support using a solution containing precursors of the metals, the phosphorus precursor and the precursor(s) of the dopant being selected from boron and/or fluorine.

The source of boron may be boric acid, preferably orthoboric acid H₃B O₃, ammonium biborate or pentaborate, boron oxide, or boric esters. The boron may, for example, be introduced by means of a solution of boric acid in a water/alcohol mixture or in a water/ethanolamine mixture.

The sources of fluorine which may be used are well known to the skilled person. As an example, the fluoride anions may be introduced in the form of hydrofluoric acid or its salts. These salts are formed with alkali metals, ammonium or an organic compound. In this latter case, the salt is advantageously formed in the reaction mixture by reaction between the organic compound and hydrofluoric acid. The fluorine may, for example, be introduced by impregnation of an aqueous solution of hydrofluoric acid or ammonium fluoride, or indeed ammonium bifluoride.

In a preferred mode, the process for the preparation of the catalyst of step a) of the process of the invention comprises the following steps:

a′) impregnating a solution containing at least one precursor of a metal from group VIB, at least one precursor of a metal from group VIII, phosphorus, optionally another dopant selected from boron and/or fluorine, onto an alumina support;

a″) optionally, drying the impregnated support obtained from step a′);

a′″) calcining the impregnated and optionally dried support so as to transform the precursors of the metals from group VIB and from group VIII into oxides.

Impregnation step a′) is carried out in accordance with the variations described above. Highly preferably, the metals from group VIB and from group VIII, the phosphorus and optional other dopant selected from boron and/or fluorine are introduced in their entirety after shaping said alumina support, by dry impregnation of said support with the aid of an aqueous impregnation solution containing precursor salts of the metals, phosphorus and optional dopant selected from boron and/or fluorine.

The drying of step a″) is generally carried out at a temperature in the range 50° C. to 180° C., preferably in the range 60° C. to 150° C. and highly preferably in the range 75° C. to 130° C. Drying is generally carried out for a period in the range 1 to 24 hours, preferably in the range 1 to 20 hours. Drying is carried out in air, or under an inert atmosphere (for example nitrogen).

The calcining of step a′″) is generally carried out at a temperature in the range 250° C. to 900° C., preferably in the range 350° C. to 750° C. The calcining period is generally in the range 0.5 hours to 16 hours, preferably in the range 1 hour to 5 hours. It is generally carried out in air. Calcining can be used to transform the precursors of the metals from groups VIB and VIII into oxides.

Before using it, it is advantageous to transform the catalyst in the oxide form (calcined) used in step a) of the process of the invention into a sulphurized catalyst in order to form its active species. This activation or sulphurization phase is carried out using methods which are well known to the skilled person, advantageously in a sulpho-reducing atmosphere in the presence of hydrogen and hydrogen sulphide.

In a preferred variation, the catalyst obtained in step a′″) undergoes a sulphurization step. The sulphurization step is advantageously carried out in an ex situ or in situ manner. The sulphurizing agents are H₂S gas or any other compound containing sulphur used for activation of hydrocarbon feeds with a view to sulphurizing the catalyst. Said compounds containing sulphur are advantageously selected from alkyldisulphides such as, for example, dimethyldisulphide (DMDS), alkylsulphides such as, for example dimethyl sulphide, n-butylmercaptan, polysulphide compounds of the tertiononoylpolysulphide type, or any other compound which is known to the skilled person and can result in good sulphurization of the catalyst. Preferably, the catalyst is sulphurized in situ in the presence of a sulphurizing agent and a hydrocarbon feed. Highly preferably, the catalyst is sulphurized in situ in the presence of a hydrocarbon feed supplemented with dimethyldisulphide.

Step b): Hydrotreatment with an Additive-Containing Catalyst

In accordance with step b) of the process of the invention, the effluent obtained from step a) is brought into contact, in the presence of hydrogen, with at least a second catalyst comprising an alumina support, phosphorus, an active phase formed by at least one metal from group VIB and at least one metal from group VIII and at least one organic compound containing oxygen and/or nitrogen, said second catalyst being prepared in accordance with a process comprising the following steps:

i) bringing at least one component of a metal from group VIB, at least one component of a metal from group VIII, phosphorus and at least one organic compound containing oxygen and/or nitrogen into contact with the support, in order to obtain a catalyst precursor;

ii) drying said catalyst precursor obtained from step i) at a temperature of less than 200° C., without subsequent calcining thereof.

The catalyst used in step b) of the invention is composed of an alumina support, phosphorus, an active phase formed by at least one metal from group VIB and at least one metal from group VIII, and an organic compound containing oxygen or nitrogen. The catalyst used in step b) is a catalyst termed an additive-containing catalyst. During its preparation, it does not undergo calcining, i.e. its active phase comprises metals from groups VIB and VIII which have not been transformed into the oxide form.

The total quantity of metal from group VIII and metal from group VIB as well as the molar ratio of the metal from group VIII to the metal from group VIB of the catalyst of step b) are in the same ranges as those described for the catalyst of step a).

The metal from group VIB present in the active phase of the catalyst used in step b) of the invention is preferably molybdenum.

The metal from group VIII present in the active phase of the catalyst used in step b) of the invention is preferably selected from cobalt, nickel and a mixture of these two elements.

Preferably, the active phase of the catalyst used in step b) is selected from the group formed by the following combinations of elements: nickel-molybdenum, cobalt-molybdenum and nickel-cobalt-molybdenum.

The additive-containing catalyst used in step b) also comprises phosphorus as the dopant. The phosphorus content of the catalyst of step b) as well as the molar ratio of phosphorus to the metal from group VIB of the catalyst of step b) are in the same ranges as those described for the catalyst of step a).

The catalyst used in step b) of the invention may advantageously further contain at least one other dopant selected from boron and/or fluorine. When the catalyst used in step b) contains boron and/or fluorine, the quantities of boron and/or fluorine are in the same ranges as those described for the catalyst of step a).

The alumina support for said catalyst used in step b) was described in the section pertaining to step a). The support for the additive-containing catalyst of step b) may be identical to or different from the support of the catalyst used in step a).

Preferably, the support for said catalyst used in step b) is constituted by alumina, preferably extruded alumina. Preferably, the alumina is gamma alumina, and said alumina support is preferably constituted by gamma alumina.

The catalyst used in step b) further contains an organic compound containing oxygen and/or nitrogen. This compound is an organic compound containing more than 2 carbon atoms and at least one oxygen and/or nitrogen atom.

The organic compound containing oxygen may be one or more compounds selected from a carboxylic acid, an alcohol, an aldehyde or an ester. By way of example, the organic compound containing oxygen may be one or more compounds selected from the group constituted by ethylene glycol, glycerol, polyethylene glycol (with a molecular weight of 200 to 1500), acetophenone, 2,4-pentanedione, pentanole, acetic acid, maleic acid, oxalic acid, tartaric acid, formic acid, citric acid and C1-C4 dialkyl succinate. The dialkyl succinate used is preferably included in the group composed of dimethyl succinate, diethyl succinate, dipropyl succinate and dibutyl succinate. Preferably, the C1-C4 dialkyl succinate used is dimethyl succinate or diethyl succinate. Highly preferably, the C1-C4 dialkyl succinate used is dimethyl succinate. At least one C1-C4 dialkyl succinate is used, preferably one alone, and preferably dimethyl succinate.

The organic compound containing nitrogen may be selected from an amine. By way of example, the organic compound containing nitrogen may be ethylene diamine or tetramethylurea.

The organic compound containing oxygen and nitrogen may be selected from an aminocarboxylic acid, an aminoalcohol, a nitrile or an amide. By way of example, the organic compound containing oxygen and nitrogen may be aminotriacetic acid, 1,2-cyclohexanediaminetetraacetic acid, mono-ethanolamine, acetonitrile, N-methylpyrrolidone, dimethylformamide or EDTA.

Preferably, the organic compound contains oxygen. Particularly preferably, the organic compound comprises at least the combination of C1-C4 dialkyl succinate, in particular dimethyl, and acetic acid. In accordance with another particularly preferred variation, the organic compound comprises at least citric acid.

The catalyst used in step b) is prepared in accordance with a process comprising the following steps:

i) bringing at least one component of a metal from group VIB, at least one component of a metal from group VIII, phosphorus and at least one organic compound containing oxygen and/or nitrogen into contact with the support, in order to obtain a catalyst precursor;

ii) drying said catalyst precursor obtained from step i) at a temperature of less than 200° C., without subsequent calcining thereof.

Contact step i) can be implemented in a number of manners.

In accordance with the first implementation of step i) of the process for the preparation of the catalyst used in step b), said components of the metals from group VIB and group VIII, phosphorus and that of said organic compound are deposited on said support by at least one co-impregnation step, preferably by dry impregnation. In accordance with this implementation, also known as “co-impregnation”, said components of the metals from group VIB and group VIII, phosphorus and the organic compound are simultaneously introduced into said support. Said first embodiment of step i) comprises carrying out one or more co-impregnation steps, each co-impregnation step preferably being followed by a drying step as described in step i″) below.

In accordance with the second embodiment of step i) of the process for the preparation of the catalyst used in step b), at least one catalytic precursor comprising at least one metal from group VIII, at least one metal from group VIB, said phosphorus and at least said alumina support are brought into contact with at least one organic compound containing oxygen and/or nitrogen. In accordance with the invention, said second embodiment is a preparation known as “post-impregnation”. In accordance with this variation, the catalyst precursor is prepared by depositing at least one component of a metal from group VIB, at least one component of a metal from group VIII and phosphorus on said support using any method known to the skilled person, preferably by dry impregnation, excess impregnation or by deposition-precipitation using methods which are well known to the skilled person. The components of the metals from groups VIB and VIII and phosphorus may be deposited by one or more impregnations, preferably followed by a drying step as described in step i″) below.

In accordance with a particularly preferred variation, the contact of step i) is carried out in accordance with the second embodiment of step i), i.e. by post-impregnation. In a particularly preferred variation, the catalyst used in step b) is prepared in accordance with the preparation process described in US 2013/008829. More precisely, step i) of the process for the preparation of the catalyst of step b) may comprise the following steps in succession which will be described in more detail below:

i′) impregnating an alumina support with at least one solution containing at least one metal from group VIB, at least one metal from group VIII and said phosphorus in order to obtain an impregnated support;

i″) drying the impregnated support obtained in step i′) at a temperature of less than 180° C. without subsequent calcining, in order to obtain a dried impregnated support;

i′″) impregnating the dried impregnated support obtained in step i″) with an impregnation solution comprising at least one organic compound containing oxygen and/or nitrogen in order to obtain an impregnated catalytic precursor;

i″″) allowing the impregnated catalytic precursor obtained in step i′″) to mature, in order to obtain said catalyst precursor.

In step i′), the metals from group VIB and from group VIII may advantageously be introduced onto the alumina support by one or more excess solution impregnations, or preferably by one or more dry impregnations and more preferably by a dry impregnation of said alumina support, using an aqueous or organic solution containing precursors of the metals. The impregnation step may be carried out in the same manner as that described for the preparation of the catalyst in the oxide form described in step a). The precursors of the metal from group VIB and from group VIII are those described for step a). Said phosphorus and the optional other dopant selected from boron and/or fluorine may be introduced in the manner described in step a). The phosphorus, boron and fluorine precursors are those described in step a).

Introduction of the metals from group VIB and from group VIII and phosphorus onto the alumina support is then followed by a step i″) for drying, during which the solvent (which is generally water) is eliminated, at a temperature in the range 50° C. to 180° C., preferably in the range 60° C. to 150° C. or in the range 65° C. to 145° C., and highly preferably in the range 70° C. to 140° C. or in the range 75° C. to 130° C. The step for drying the dried impregnated support obtained thereby is never followed by a step for calcining in air at a temperature of more than 200° C.

Preferably, in step i′), said impregnated support is obtained by dry impregnation of a solution comprising precursors of metals from group VIB and from group VIII, and phosphorus onto an alumina support which has been calcined and shaped, followed by drying at a temperature of less than 180° C., preferably in the range 50° C. to 180° C., preferably in the range 60° C. to 150° C. and highly preferably in the range 75° C. to 130° C. A dried impregnated support is thus obtained at the end of step i″).

In accordance with step i′″), said dried impregnated support is impregnated with an impregnation solution comprising at least one organic compound containing oxygen and/or nitrogen, preferably C1-C4 dialkyl succinate (and in particular dimethyl succinate) and acetic acid. In another variation, the impregnation solution of step i′″) preferably comprises citric acid. The impregnation solution comprising at least said organic compound is preferably an aqueous solution.

The molar ratio of the organic compound(s) containing oxygen and/or nitrogen over the impregnated element(s) from group VIB of the catalytic precursor engaged on the catalyst is in the range 0.05 to 2 mol/mol, preferably in the range 0.1 to 1.8 mol/mol, preferably in the range 0.15 to 1.5 mol/mol before the drying of step ii). When the organic component is a mixture of C1-C4 dialkyl succinate (and in particular dimethyl succinate) and acetic acid, said components are advantageously introduced into the impregnation solution of step i′″) of the process of the invention in a quantity corresponding to:

-   -   a molar ratio of dialkyl succinate (for example dimethyl) to         impregnated element(s) from group VIB of the catalytic precursor         in the range 0.05 to 2 mol/mol, preferably in the range 0.1 to         1.8 mol/mol, more preferably in the range 0.15 to 1.5 mol/mol;     -   a molar ratio of acetic acid to impregnated element(s) from         group VIB of the catalytic precursor in the range 0.1 to 5         mol/mol, preferably in the range 0.5 to 4 mol/mol, more         preferably in the range 1.3 to 3 mol/mol and highly preferably         in the range 1.5 to 2.5 mol/mol.

Said organic compound(s) may advantageously be deposited in one or more steps, either by slurry impregnation or by excess impregnation or by dry impregnation, or by any other means which is known to the skilled person.

In accordance with step i′″), the organic compound containing oxygen or nitrogen is introduced onto the dried impregnated support by at least one impregnation step, preferably by a single impregnation step, and particularly preferably by a single dry impregnation step.

In accordance with step i″″) of the preparation process of the invention, the impregnated catalytic precursor obtained from step i′″) undergoes a maturation step. It is advantageously carried out at atmospheric pressure and at a temperature in the range 17° C. to 50° C., and generally a maturation period in the range ten minutes to forty-eight hours, preferably in the range thirty minutes to five hours is sufficient. Longer times are not excluded. A catalyst precursor is thus obtained at the end of step i″″).

In accordance with step ii) of the preparation process of the invention, the catalyst precursor obtained from step i) undergoes a drying step at a temperature below 200° C., without subsequently calcining it.

The drying step ii) of the process of the invention is advantageously carried out using any technique which is known to the skilled person. It is advantageously carried out at atmospheric pressure or under reduced pressure. Preferably, this step is carried out at atmospheric pressure.

This step ii) is advantageously carried out at a temperature in the range 50° C. to less than 200° C., preferably in the range 60° C. to 180° C. and highly preferably in the range 80° C. to 160° C.

Step ii) is advantageously carried out in a flushed bed using air or any other hot gas. Preferably, when drying is carried out in a fixed bed, the gas used is either air or an inert gas such as argon or nitrogen. Highly preferably, drying is carried out in a flushed bed in the presence of nitrogen.

Preferably, this step lasts in the range 30 minutes to 4 hours, preferably in the range 1 hour to 3 hours.

At the end of step ii) of the process of the invention, a dry catalyst is obtained which is also known as the “additive-containing catalyst”, which does not undergo any subsequent calcining step in air, for example at a temperature of more than 200° C.

Before using it, it is advantageous to transform the additive-containing catalyst used in step b) into a sulphurized catalyst in order to form its active species. This activation or sulphurization phase is carried out using methods which are well known to the skilled person, and advantageously in a sulpho-reductive atmosphere in the presence of hydrogen and hydrogen sulphide.

At the end of step ii) of the process of the invention, said dried additive-containing catalyst obtained thus advantageously undergoes a sulphurizing step iii), without an intermediate calcining step.

Said additive-containing catalyst is advantageously sulphurized ex situ or in situ. The same sulphurization agents as those described for the catalyst in the oxide form in step a) may be used.

When sulphurization is carried out in situ, sulphurization of the catalyst of step b) is advantageously carried out at the same time as sulphurization of the catalyst of step a).

Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The preceding preferred specific embodiments are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever.

In the foregoing and in the examples, all temperatures are set forth uncorrected in degrees Celsius and, all parts and percentages are by weight, unless otherwise indicated.

The entire disclosures of all applications, patents and publications, cited herein and of corresponding French application No. 13/61.801, filed Nov. 28, 2013 are incorporated by reference herein.

EXAMPLES

The following examples demonstrate that a hydrotreatment process in accordance with the invention using a “catalyst in the oxide form/additive-containing catalyst” concatenation has improved activity and improved stability compared with a process using only additive-containing catalysts.

Preparation of Catalysts A, B, C and D:

The following 4 catalysts were prepared:

-   -   catalyst A: calcined NiMoP/alumina catalyst     -   catalyst B: calcined CoMoP/alumina catalyst     -   catalyst C: NiMoP/alumina catalyst supplemented with acetic acid         and dimethyl succinate (post-impregnation)     -   catalyst D: CoMoP/alumina catalyst supplement with citric acid         (co-impregnation)

Preparation of Support

A matrix composed of an ultrafine tabular boehmite or alumina gel was used, sold by Condéa Chemie GmbH. This gel was mixed with an aqueous solution containing 66% nitric acid (7% by weight of acid per gram of dry gel) then mixed for 15 minutes. At the end of this mixing, the paste obtained was passed through a die having cylindrical orifices with a diameter equal to 1.6 mm. The extrudates were then dried overnight at 120° C. and calcined at 600° C. for 2 hours in moist air containing 50 g of water per kg of dry air. Thus, extrudates of the support were obtained which had a specific surface area of 300 m²/g. X ray diffraction analysis revealed that the support is solely composed of low crystallinity cubic gamma alumina.

Catalyst A: Calcined NiMoP/Alumina Catalyst

In the case of catalyst A based on nickel, the nickel, molybdenum and phosphorus were added to the alumina support described above which was in the form of extrudates. The impregnation solution was prepared by hot dissolving the molybdenum oxide and nickel hydroxycarbonate in the phosphoric acid solution in aqueous solution with the aim of producing an approximately 4/22/5 formulation, expressed as the % by weight of oxides of nickel and molybdenum and as the % by weight of phosphoric anhydride with respect to the quantity of dry matter in the final catalyst. After dry impregnation, the extrudates were allowed to mature in a water-saturated atmosphere for 8 h, then they were dried overnight at 90° C. Calcining at 450° C. for 2 hours resulted in catalyst A.

The final composition of catalyst A, expressed in the oxide form, was then as follows: MoO₃=22.0±0.2 (% by weight), NiO=4.1±0.1 (% by weight) and P₂O₅=5.0±0.1 (% by weight).

Catalyst B: Calcined CoMoP

In the case of catalyst B based on cobalt, the cobalt, molybdenum and phosphorus were added to the alumina support described above which was in the form of extrudates. The impregnation solution was prepared by hot dissolving the molybdenum oxide and cobalt carbonate in the phosphoric acid solution in aqueous solution with the aim of producing an approximately 4/22/5 formulation, expressed as the % by weight of oxides of cobalt and molybdenum and as the % by weight of phosphoric anhydride with respect to the quantity of dry matter in the final catalyst. After dry impregnation, the extrudates were allowed to mature in a water-saturated atmosphere for 8 h, then they were dried overnight at 90° C. Calcining at 450° C. for 2 hours resulted in catalyst B.

The final composition of catalyst B, expressed in the oxide form, was then as follows: MoO₃=22.0±0.2 (% by weight), CoO=4.1±0.1 (% by weight) and P₂O₅=5.0±0.1 (% by weight).

Catalyst C: NiMoP/Alumina Catalyst Supplemented with Acetic Acid and Dimethyl Succinate (DMSU)

In the case of catalyst C based on nickel, the nickel, molybdenum and phosphorus were added to the alumina support described above in the form of extrudates. The impregnation solution was prepared by hot dissolving molybdenum oxide and nickel hydroxycarbonate in the solution of phosphoric acid in aqueous solution with the aim of obtaining an approximately 5/25/6 formulation expressed as the % by weight of oxides of nickel and molybdenum and as the % by weight of phosphoric anhydride with respect to the quantity of dry matter of the final catalyst. After dry impregnation, the extrudates were allowed to mature in a water-saturated atmosphere for 8 h, then they were dried overnight at 90° C. The dried impregnated support for catalyst C was then supplemented by dry impregnation of a solution containing a mixture of dimethyl succinate (DMSU) and acetic acid (75% pure). The molar ratios were as follows: DMSU/Mo=0.85 mol/mol, DMSU/acetic acid=0.5 mol/mol. Next, the catalyst underwent a maturing step for 3 h at 20° C. in air, followed by drying in a flushed bed type oven at 120° C. for 3 h.

The final composition of catalyst C, expressed in the oxide form, was thus as follows: MoO₃=25.1±0.2 (% by weight), NiO=5.1±0.1 (% by weight) and P₂O₅=6.0±0.1 (% by weight).

Catalyst D: CoMoP/Alumina Catalyst Supplemented with Citric Acid

In the case of catalyst D based on cobalt, the cobalt, molybdenum and phosphorus were added to the alumina support described above in the form of extrudates. The impregnation solution was prepared by hot dissolving molybdenum oxide and cobalt hydroxide and citric acid in the solution of phosphoric acid in aqueous solution with the aim of obtaining an approximately 4/22/5 formulation, expressed as the % by weight of oxides of cobalt and molybdenum and as the % by weight of phosphoric anhydride with respect to the quantity of dry matter of the final catalyst. The quantity of citric acid, expressed as the molar ratio with respect to molybdenum, was: citric acid/Mo=0.4 mol/mol. After dry impregnation, the extrudates were allowed to mature in a water-saturated atmosphere for 8 h, then they were dried overnight at 90° C. then dried in a flushed bed type oven at 140° C. for 3 h.

The final composition of catalyst D, expressed in the oxide form, was thus as follows: MoO₃=22.4±0.2 (% by weight), CoO=4.1±0.1 (% by weight) and P₂O₅=5.0±0.1 (% by weight).

Evaluation of Various Concatenations of Catalysts A, B, C and D in the Hydrotreatment of a Straight-Run Diesel/LCO Mixture

The feed used was a mixture of 70% by volume of diesel obtained from atmospheric distillation (straight-run) and 30% by volume of coker gas with a WAT of 285° C. The characteristics of the feed were as follows: density (at 15° C.) 0.8486, sulphur 1.06% by weight, nitrogen 410 ppm, basic nitrogen 200 ppm, aromatics (UV) 29% by weight.

-   -   Simulated distillation:

IP: 150° C.  5%: 200° C. 10%: 220° C. 50%: 283° C. 70%: 307° C. 90%: 337° C.

The test was carried out in an isothermal pilot reactor with a fixed flushed bed, with the fluids moving from bottom to top. The reactor comprised two catalytic zones for evaluating various concatenations of the catalysts A, B, C and D. The feed passed initially over the first zone charged with the first catalyst, then the second zone charged with the second catalyst.

In accordance with Example 1 (not in accordance with the invention), the entirety of the two catalytic zones (100% of the volume) contained additive-containing catalyst (catalyst C).

In accordance with Examples 2 and 3 (in accordance with the invention), the first zone was charged with a calcined catalyst (catalysts A or B: 30% of the volume), then the second with an additive-containing catalyst (catalyst C: 70% of the volume).

In accordance with Example 4 (not in accordance with the invention), the two zones were charged with an additive-containing catalyst (catalyst D: 30% of the volume, then catalyst C: 70% of the volume).

In accordance with Example 5 (not in accordance with the invention), the first zone was charged with an additive-containing catalyst (catalyst C: 70% of the volume), then the second with a calcined catalyst (catalyst A: 30% of the volume).

After in situ sulphurization at 350° C. in the unit pressurized with diesel to which 2% by weight of dimethyldisulphide had been added, the hydrodesulphurization test was carried out under the following operating conditions: a total pressure of 5 MPa (50 bar), a H₂/feed ratio of 380 L/L and a HSV of 1.5 h⁻¹.

The temperature was adjusted so as to obtain a sulphur content of 10 ppm at the reactor outlet. The following table shows the temperature necessary to obtain a sulphur content of 10 ppm for the various concatenations of the catalysts A, B, C and D. A high catalytic activity is expressed by a low temperature T1. A high stability is expressed by a low temperature T2 after an operating period (in this case 1000 hours).

The results clearly show that the “catalyst in the oxide form/additive-containing catalyst” concatenation (Examples 2 and 3) can be used to obtain a catalytic activity which is higher and a higher stability than a concatenation of “additive-containing catalysts” alone (Examples 1 and 4) or an “additive-containing catalyst/catalyst in the oxide form” concatenation (Example 5).

TABLE temperature required to obtain a 10 ppm content at the reactor outlet Catalyst charged into the reactor Example (first zone/second zone) T1* T2** 1, 100% vol catalyst C (additive- 345° C. 348° C. comparative containing NiMoP) 2, 30% vol catalyst A (calcined 342° C. 343° C. in accordance NiMoP) + 70% vol catalyst C with the (additive-containing NiMoP) invention 3, 30% vol catalyst B (calcined 343° C. 345° C. in accordance CoMoP) + 70% vol catalyst C with the (additive-containing NiMoP) invention 4, 30% vol catalyst D (additive- 348° C. 351° C. comparative containing CoMoP) + 70% vol catalyst C (additive-containing NiMoP) 5, 70% vol catalyst C (additive- 352° C. 357° C. comparative containing NiMoP) + 30% vol catalyst B (calcined NiMoP) *T1: temperature after 300 h operation **T2: temperature after 1000 h operation

In the case of Examples 2, 3 and 4, the values for hydrodenitrogenation (HDN) as a % of the first zone were as follows; the conditions were as mentioned above:

-   -   catalyst A (calcined NiMoP): HDN (%)=70% the residual nitrogen         content (total) was of the order of 150 ppm, mainly in the form         of non-basic carbazole species     -   catalyst B (calcined CoMoP): HDN (%)=67%     -   catalyst C (NiMoP supplemented with DMSU/acetic acid): HDN         (%)=63%     -   catalyst D (CoMoP supplemented with citric acid): HDN (%)=58%.

It will be observed that the calcined catalysts (catalysts A and B) can be used to carry out more intense HDN than an additive-containing catalyst (catalysts C and D).

The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and/or operating conditions of this invention for those used in the preceding examples.

From the foregoing description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions. 

1. A process for the hydrotreatment of a hydrocarbon feed containing nitrogen-containing compounds in an amount of more than 150 ppm by weight and having a weighted average temperature in the range 250° C. to 380° C., comprising the following steps: a) bringing said hydrocarbon feed into contact, in the presence of hydrogen, with at least one first catalyst comprising an alumina support, phosphorus, and an active phase formed by at least one metal from group VIB in the oxide form and at least one metal from group VIII in the oxide form, said first catalyst being prepared in accordance with a process comprising at least one calcining step; b) bringing the effluent obtained in step a) into contact, in the presence of hydrogen, with at least one second catalyst comprising an alumina support, phosphorus, an active phase formed by at least one metal from group VIB and at least one metal from group VIII, and at least one organic compound containing oxygen and/or nitrogen, said second catalyst being prepared in accordance with a process comprising the following steps: i) bringing at least one component of a metal from group VIB, at least one component of a metal from group VIII, phosphorus and at least one organic compound containing oxygen and/or nitrogen into contact with the support, so as to obtain a catalyst precursor; ii) drying said catalyst precursor obtained from step i) at a temperature of less than 200° C., without subsequent calcining; in order to obtain a hydrotreated effluent.
 2. The process according to claim 1 in which, for the catalyst of step a) or b), the metal from group VIB is molybdenum and the metal from group VIII is selected from cobalt, nickel and a mixture of these two elements.
 3. The process according to claim 1 in which, for the catalyst of step a) or b), the quantity of metal from group VIB is in the range 5% to 40% by weight of oxide of the metal from group VIB with respect to the total catalyst weight, the quantity of metal from group VIII is in the range 1% to 10% by weight of oxide of the metal from group VIII with respect to the total catalyst weight, and the quantity of phosphorus is in the range 0.1% to 10% by weight of P₂O₅ with respect to the total catalyst weight.
 4. The process according to claim 1, in which the catalyst of step a) or b) further contains at least one dopant selected from boron and fluorine and a mixture of boron and fluorine.
 5. The process according to claim 1, in which the organic compound is one or more selected from a carboxylic acid, an alcohol, an aldehyde, an ester, an amine, an aminocarboxylic acid, an aminoalcohol, a nitrile or an amide.
 6. The process according to claim 5, in which the organic compound is one or more selected from ethylene glycol, glycerol, polyethylene glycol (with a molecular weight of 200 to 1500), acetophenone, 2,4-pentanedione, pentanole, acetic acid, maleic acid, oxalic acid, tartaric acid, formic acid, citric acid and C1-C4 dialkyl succinate.
 7. The process according to claim 5, in which the organic compound comprises at least the combination of C1-C4 dialkyl succinate and acetic acid.
 8. The process according to claim 5, in which the organic compound comprises at least citric acid.
 9. The process according to claim 1, in which the catalyst of step a) or b) has also undergone a sulphurizing step.
 10. The process according to claim 1, in which the quantity of basic nitrogen in the feed is 50 ppm or more.
 11. The process according to claim 1, in which the feed is a feed obtained from catalytic cracking, a coker or from visbreaking.
 12. The process according to claim 1, in which each of steps a) and b) is carried out at a temperature in the range 180° C. to 450° C., at a pressure in the range 0.5 to 10 MPa, at an hourly space velocity in the range 0.1 to 20 h⁻¹ and with a hydrogen/feed ratio, expressed as the volume of hydrogen measured under normal temperature and pressure conditions, per volume of liquid feed in the range 50 L/L to 2000 L/L.
 13. The process according to claim 1, in which step a) is carried out in a first zone containing the first catalyst which occupies a volume V1, and step b) is carried out in a second zone containing the second catalyst which occupies a volume V2, the distribution of the volumes, V1/V2, being in the range 10% by volume/90% by volume to 50% by volume/50% by volume for the first and second zone respectively.
 14. The process according to claim 1, in which step i) of step b) comprises the following steps in succession: i′) impregnating an alumina support with at least one solution containing at least one metal from group VIB, at least one metal from group VIII and said phosphorus in order to obtain an impregnated support; i″) drying the impregnated support obtained in step i′) at a temperature of less than 180° C. without subsequent calcining in order to obtain a dried impregnated support; i′″) impregnating the dried impregnated support obtained in step i″) with an impregnation solution comprising at least one organic compound containing oxygen and/or nitrogen in order to obtain an impregnated catalytic precursor; i″″) allowing the impregnated catalytic precursor obtained in step i′″) to mature, in order to obtain said catalyst precursor.
 15. The process according to claim 1, in which the effluent obtained in step a) undergoes a separation step in order to separate a heavy fraction and a light fraction containing the H₂S and NH₃ formed during step a), said heavy fraction then being introduced into step b). 